Question

How to extract the second row of a 2D vector in C++

Answer 1

#include <iostream>
#include <vector>

int main() {
    std::vector<std::vector<int>> matrix {
        { 1, 4, 8, 9 },
        { 8, 3, 5, 1 },
        { 7, 0, 6, 2 }
    };

    std::vector<int>& secondRow = matrix[1];
    
    for (int element : secondRow) {
        std::cout << element << " ";
    }
    std::cout << "\n";
    
    matrix[1][0] = 790;
    
    for (int element : secondRow) {
        std::cout << element << " ";
    }
}

   
    
/*
run:

8 3 5 1 
790 3 5 1   

*/

 

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Answer 2

#include <iostream>
#include <vector>

int main() {
    std::vector<std::vector<int>> matrix {
        { 1, 4, 8, 9 },
        { 8, 3, 5, 1 },
        { 7, 0, 6, 2 }
    };

    std::vector<int> secondRow; 
    secondRow.insert(secondRow.begin(), matrix[1].begin(), matrix[1].end());
    
    for (int element : secondRow) {
        std::cout << element << " ";
    }
    std::cout << "\n";
    
    matrix[1][0] = 790;
    
    for (int element : secondRow) {
        std::cout << element << " ";
    }
}

   
    
/*
run:

8 3 5 1 
8 3 5 1  

*/

 

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